JP2015097222A - Superconductive magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a superconductive magnet with large stored energy capable of being protected at quench occurrence.SOLUTION: The superconductive magnet is constituted of plural superconducting coil blocks (2a, 2b) each being connected to protective resistors (7a, 7b and 7c, 7d) in parallel, and which are connected in series to each other being interposed by switches (3, 5a, 5b) inserted between the coil blocks (2a, 2b). Each of the protective resistors is provided with a protective resistor short circuit switch (8a, 8b) for causing a short circuit. When a quench occurs, the switches (3, 5a, 5b) are cut off in such a state the protective resistor short circuit switches (8a, 8b) are ON; and after cutting off the switches (3, 5a, 5b), the protective resistor short circuit switches (8a, 8b) are turned OFF.

Description

  The present invention relates to a superconducting magnet using a superconducting magnet protection circuit.

  When a superconductor having no direct current electric resistance is used, it is possible to pass a current at a high current density. Therefore, an electromagnet that generates a strong magnetic field using this is realized. Electromagnets made of superconducting wires (hereinafter referred to as superconducting magnets) are used in NMR (Nuclear Magnetic Resonance) spectrometers, MRI (Magnetic Resonance Imaging) magnets, research accelerator magnets, etc. Yes.

  The superconducting magnet is cooled to a very low temperature and maintained in a superconducting state, but at a very low temperature, the specific heat is an order of magnitude smaller than that at room temperature. Quenching with normal conducting transition may occur.

  Superconducting magnets that generate a magnetic field store energy in the form of magnetism, but when quenching occurs and superconducting magnets generate electrical resistance, the energy stored in the resistance is consumed. Become. When the accumulated energy is large and energy is consumed locally, the temperature of the region quenched by Joule heat rises rapidly and eventually burns out.

  Therefore, the superconducting magnet requires a protection mechanism for preventing the superconducting magnet from burning when a quench occurs. In general, a resistance called a protective resistance is connected in parallel to the superconducting magnet, and energy is quickly changed to heat and consumed by the protective resistance, thereby suppressing a local temperature rise inside the superconducting magnet.

  As another method, heat is applied to a portion that is not quenched by the heater, the resistance generation region of the superconducting magnet is quickly expanded, and energy is consumed in a wide region rather than a local temperature, thereby causing a local temperature There is also a protection method called quenchback that suppresses the rise.

  In any case, it is important to prevent the burnout by consuming energy in a wider area without causing heat generation in the local area where the quench occurs, and by quickly attenuating the current flowing in the magnet by external resistance. It becomes.

  In order to prevent burning of the magnet, it is necessary to quickly attenuate the current flowing through the magnet. When the current is drawn from the magnet, an induced voltage accompanying the change in current is generated in the magnet in addition to the resistive voltage in the quenched region. When the current is rapidly attenuated, the induced voltage increases, and there is no electrical insulation of the magnet.

  When the scale of a magnet becomes larger, it is difficult to protect the whole magnet at once because the generated voltage is too large. Divide the composed magnet, and protect the individual divided small magnets with protective resistance. It is necessary to perform division protection. By performing the division, voltage generation in each magnet can be reduced. In addition, when divided protection is used, the current decay time constant in the protection circuit of each magnet can be set appropriately, and the timing of the protection operation can be adjusted, so the overall generated voltage is kept lower than the overall collective protection. It is possible.

  However, even with split protection, the maximum potential (ground voltage) of the magnet as seen from the ground potential is lifted by adding the voltages generated by the individual protection circuits. It will be difficult to ensure.

  Non-Patent Document 1 and Patent Document 1 disclose a method of suppressing this ground voltage even in a large magnet. In this method, there is no resistance in the main circuit during normal operation, and resistance is generated in the main circuit during the magnet protection operation after the quench occurs. By alternately arranging the inductance and resistance of the coil in the main circuit, the negative voltage generated in the inductance portion and the positive voltage generated in the resistance portion are canceled with each other, thereby suppressing the ground voltage.

JP-A-9-93800

"OPERATING EXPERIENCE OF TORE SUPRA SUPERCONDUCTING MAGNETS", Turck, B. et al., Fusion Engineering, 1993., 15th IEEE / NPSS Symposium on (Volume: 1)

  The ground voltage can be reduced by the magnet protection method disclosed in Non-Patent Document 1, Patent Document 1, and the like. However, this method is characterized in that the negative voltage generation due to the inductance and the positive voltage generation due to the resistance are cancelled, so it is necessary to balance the negative voltage and the positive voltage.

  If a plurality of magnets having the same shape are arranged and the inductance values are approximately the same, the induced electromotive force generated is the same, and therefore the design is relatively easy. However, if there are coils with different inductance values, the magnitude of the induced electromotive force is different, making the design difficult. In this case, the voltage can be canceled by making a difference between the resistance values inserted in series so as to cancel the induced voltage according to the magnitude of the inductance. However, since the current value and current decay rate during the magnet protection operation after quenching change with time, it is impossible in principle to always balance the induced electromotive force and the resistance voltage. The design in which the inductance and resistance are arranged alternately is certainly effective in suppressing the ground voltage, but the magnets of the constituent elements are different, and the magnet with a large stored energy as a whole is the ground for this method. There is a limit to voltage suppression.

  An object of the present invention is to provide a method for protecting a superconducting magnet regardless of the configuration of the magnet and the magnitude of stored energy.

  In the superconducting magnet of the present invention, a plurality of coil blocks are connected in series across a switch to form a main circuit, and protective resistances are connected in parallel to the individual coil blocks. Has a configuration in which switches for short-circuiting are connected in parallel. This protective resistor is grounded at the midpoint. When a quench occurs and the protection operation of the magnet starts, the short-circuit switch provided in the protection resistor is closed. After the individual circuit blocks are disconnected by opening the main circuit switch, the short-circuit switch is opened. To.

  According to the present invention, it is possible to provide a protection circuit in which the ground voltage of a normal conducting magnet is restricted to an allowable value or less regardless of the size of the magnet.

It is a basic circuit diagram of the superconducting magnet protection circuit of the present invention. It is a circuit diagram which shows the structure of the protection resistance short circuit switch of this invention. It is a circuit diagram which shows the structure method of the high voltage | pressure-resistant protective resistance short circuit switch of this invention. It is a circuit diagram which shows the structure of the main circuit division | segmentation switch or power supply cutoff switch of this invention. It is a circuit diagram which shows another example of a structure of the main circuit parting switch of this invention, or a power cutoff switch. It is a circuit diagram which shows an example of a structure of the main circuit parting switch or power supply cutoff switch which enables control of the current commutation time of this invention. It is a circuit diagram which shows an example of a structure of the snubberless main circuit disconnection switch or power supply cutoff switch which enables control of the current commutation time of this invention. It is a circuit diagram which shows an example of the form of the whole circuit of this invention. It is a circuit diagram which shows another example of the form of the whole circuit of this invention. It is a circuit diagram which shows another basic concept of the magnet protection circuit of this invention. It is a circuit diagram which shows the example of the switch drive circuit for ensuring the time difference of switch operation | movement without control of the timing of this invention.

  The present invention relates to a protection circuit for a superconducting magnet, and relates to a protection circuit for a superconducting magnet operated in a power supply driving mode.

  In the superconducting magnet protection circuit of the present invention, a protection resistor is coupled to each superconducting coil constituting the superconducting magnet to form a current attenuating circuit. In a normal operation state, these superconducting coils are connected via a switch. Are excited in series. When a quench occurs, the switches that connect the individual circuits are turned off to make them independent, and the grounding point is grounded in each circuit, so that a protection circuit that suppresses the ground voltage in any large magnet can be reduced. realizable.

  Embodiments according to the present invention will be described below. However, the present invention is not limited to the embodiments taken up here, and can be appropriately combined and improved without departing from the scope of the invention.

  The superconducting magnet protection circuit according to the present invention is a superconducting magnet configured by connecting a plurality of coil blocks in series, and this coil block has a configuration in which one or a plurality of coils are connected in series. A protection resistance circuit is connected in parallel to the block to form a current decay loop. This coil block is connected in series via a switch and is excited by a direct current source. Furthermore, a protective resistor short-circuit switch is connected in parallel to the protective resistor, and it is configured to change the resistance value in the coil block protection circuit by short-circuiting all or part of the protective resistor by turning on the switch. ing.

  In the operation of the protection circuit of the present invention, all the switches inserted in the main circuit are turned on in the steady state, and the coil is excited by a continuous current from the direct current source. When the quench occurs, at the moment when the switch inserted in the main circuit is turned off, the switch connected in parallel to the protection resistor is in the ON state, so that the resistance of the protection circuit is kept small. When one of the switches inserted in the main circuit is turned off, the current that has flowed continuously through the main circuit flows into the protection resistor circuit, and after all the switches inserted in the main circuit are turned off, the protection circuit The switch that has been short-circuited is turned off.

  In addition, the switch inserted in the main circuit and the switch that short-circuits the protective resistance are configured by connecting a single switch or a plurality of switches in series, such as a switch having a contact such as an electromagnetic contactor, an IGBT, Consists of single or combination of semiconductor switches such as MOSFET and bipolar transformer.

  Each switch is appropriately provided with a snubber circuit (including an arbitrary voltage suppression circuit, a diode for voltage clipping, and an arrester) for suppressing generation of a high voltage when the switch is turned off.

  In addition, when a plurality of switches are connected in series, a resistance smaller than the off-resistance of the switch is set so that the voltage sharing to the individual switches connected in series when the switch is off is a desired sharing ratio. A voltage divider connected in parallel to each switch is provided.

  When the switch inserted in the main circuit is an electromagnetic contactor, it is important to suppress the generation of a high voltage when the current is interrupted when a large current is applied. Insert a semiconductor switch element such as a MOSFET into the main circuit, control the gate voltage, and gently transfer the current that flows continuously to the main circuit to the protection circuit loop. It is also possible to suppress the generation of a high voltage in the electromagnetic contactor by making the value small or zero.

  In addition, by grounding at the midpoint of each protection resistance, the voltage (absolute value) of the maximum ground voltage of each protection circuit is always generated at each superconducting coil (inductive voltage and resistance at the quench section). Half of the total voltage). Depending on the value of the protective resistance and the way the protective resistance short-circuit switch is installed, current flows to other protective circuits through the ground circuit at the midpoint of the protective resistance. It may be grounded through a suitable grounding resistor, or a switch may be attached and grounded at an appropriate switch timing of the quench protection operation (preferably after the main circuit is completely disconnected and before the protective resistor short-circuit switch is opened).

The present invention will be specifically described with reference to the drawings.
(Superconducting magnet specifications)
We designed a protection circuit for a large superconducting magnet with a generated magnetic field of 12T. The magnet has a multilayer coil configuration composed of Nb3Sn and NbTi, and is composed of four Nb3Sn coils on the inner side and six NbTi coils on the outer side. The operating current of the magnet is 700A and the stored energy is about 30MJ. Magnet protection was performed by dividing into two blocks of Nb3Sn coil and NbTi coil. Considering the voltage generation at the time of quenching and the temperature rise at the hot spot, the ground insulation design in the Nb3Sn coil block was 1.2 kV, and the ground insulation in the NbTi coil block was 2.5 kV.

  Hereinafter, description will be made using examples.

(Basic configuration of superconducting magnet protection circuit)
FIG. 1 shows a basic circuit diagram of a superconducting magnet protection circuit.

Two coil blocks (2a, 2b) in which two coils (1a, 1b and 1c, 1d) are connected in series are connected via a main circuit disconnecting switch (3) and connected to a direct current source (4) Yes. A power cutoff switch (5a, 5b) for disconnecting the power source and the coil is inserted between the direct current source and the coil. The DC current source (4) is provided with a power source protection resistor or a power source internal resistor (6) for protecting the power source inside or outside. The coil blocks (2a, 2b) are provided with protective resistors (7a, 7b and 7c, 7d) in order to form a closed circuit for attenuating current during quenching. The protective resistors (7a, 7b and 7c, 7d) of the respective coil blocks (2a, 2b) are provided with protective resistor short-circuit switches (8a, 8b) in parallel so as to be short-circuited when viewed from the coil block. Ground at the midpoint of the protective resistor installed in each coil block. A main circuit is formed by the coil block (2a, 2b), the direct current source (4), the main circuit disconnecting switch (3), and the power cutoff switch (5a, 5b).
(Operation sequence)
Next, the magnet protection operation after the occurrence of quenching will be described. During steady operation, the coil blocks (2a, 2b) are driven by the DC current source (4), so the power shut-off switches (5a, 5b) are closed, and the main circuit disconnect switch (3) is also closed. State. During steady operation, the protection circuit short-circuit switches (8a, 8b) can be either closed or open, but they must be closed from the viewpoint of guaranteeing protection without the switch timing control described below. It is.

  Although it is necessary to stop the supply of current from the DC current source (4) to the coil immediately after the quench occurs, the protective resistance short-circuit switches (8a, 8b) are closed before this operation. If the operation is always performed in the closed state even during steady operation, there is no need to re-open this switch.

  Next, an operation for stopping the supply of current from the DC current source (4) is performed. In order to stop the energy input, the power cut-off switches (5a, 5b) and the main circuit cut-off switch (3) are cut off (open). Since it is a series circuit, the supply of current from the DC current source (4) to the coil stops when any of these switches is interrupted. In the description of the basic circuit, there is no functional difference between these switches, so there is no need to pay attention to the timing of the operation for turning off the switches.

  After the main circuit disconnect switch (3) and the power shut-off switch (5a, 5b) are completely opened, the protective resistance short-circuit switches (8a, 8b) are opened.

By the above operation, each coil block operates as an independent protection circuit installed at the midpoint.
(Operating principle)
In the divided protection method that divides and protects the coil, the voltage generated per coil block can be reduced by finely dividing it, but the circuit itself is connected and the ground voltage is the voltage generated in each block. Since they are added, the ground voltage does not decrease to 1 / n even if divided into n. However, if the individual protection circuits are independent, it is clear that the ground voltage is reduced by the division. By cutting off the main circuit dividing switch and the power cut-off switch to divide the circuit, each protection circuit can be operated independently.

  However, the protection circuit is not established simply by turning off the main circuit dividing switch or the power cutoff switch. Suppose that there is no protective resistance short-circuit switch in the circuit of FIG. After detecting the quench, shut off the main circuit disconnect switch and the power shut-off switch. Since the time difference between the switch operations cannot be zero, the other switches remain connected at the moment when one of the switches is turned off.

  On the other hand, since these switches are inserted in series in the main circuit, the protection operation is started in each coil block at the moment when one of the switches is turned off (the coil current flows into the protection resistance circuit). At the moment when the current flows into the protective resistance, a voltage of the product of the current flowing through the coil block and the protective resistance is instantaneously generated, and the voltage decreases as the current decays. Since the protective resistance should be designed to be large as long as the electrical insulation can withstand in order to quickly consume the magnet energy, a large voltage is generated at the start of the protective operation. Therefore, the voltages generated in the individual protection circuits are added while the switch is connected without being cut off, and the ground voltage is increased.

  As described above, the ground voltage cannot be suppressed by simply inserting a switch in the main circuit and dividing the circuit. Therefore, in order to establish the circuit dividing method, a mechanism that does not generate a high voltage even if there is a time difference in the operation of the switch inserted in the main circuit is necessary.

  Since a voltage is generated in each protection circuit at the moment when any one of the switches of the main circuit is turned off, the problem of the time difference of the switch operation can be solved by reducing this voltage. Since the generated voltage at the start of the protection operation is determined by the product of the current flowing through the coil and the protection resistance, the generation of a high voltage can be suppressed by reducing the value of the protection resistance.

However, the protective resistance cannot be made very small because the coil burns out if the energy stored in the coil must be quickly dissipated as Joule heat. Therefore, at the moment when the switch inserted in the main circuit is turned off, the protective resistor is short-circuited by the protective resistor short-circuit switch to make it zero, and after all the switches of the main circuit are completely cut off, the protective resistor short-circuit switch The problem can be solved if the protective resistance works by turning off.
(Protection resistance short-circuit switch)
Next, the protective resistance short-circuit switch will be described. The protective resistance short-circuit switch does not pass current in the steady operation state, and when the magnet is protected after the quench occurs, the current is passed only at the moment of switching off the main circuit switch, and the main circuit switch is turned off. After that, no current flows. For this reason, the on-resistance of the switch does not have to be so small, and the heat generated by the voltage drop at the switch does not have to be so much concerned. Further, the protective resistance short-circuit switch needs to be quickly turned off after the switch inserted into the main circuit is turned off, and needs to be excellent in controllability.

  Therefore, any type of switch may be used, but it is optimal to use a semiconductor switch that can be easily cut off even when a direct current flows. There is an IGBT as such a switch. FIG. 2 shows a configuration example of the protective resistance short-circuit switch. The switch is connected to the IGBT (9) with a snubber (10) that suppresses the generation of a high voltage when the switch is off.

  The snubber may be a CR snubber as shown or other forms. If the voltage generated at switch-off is not a problem for the elements in the circuit including the superconducting coil, it is not necessary to mount the snubber.

  In addition, since the withstand voltage that can be applied between the collector and the emitter is large and the diode in the reverse direction is generally formed inside the IGBT element having a large current capacity, the diode is also illustrated. A 3.3kV IGBT module that can handle large voltages is commercially available.

  In the present embodiment, the maximum generated voltage in the Nb3Sn circuit is about 2.4 kV, and the maximum voltage circuit in the NbTi circuit is about 5 kV. Therefore, an IGBT capable of interrupting it is necessary. The maximum voltage of a generally available IGBT is 3.3 kV, which exceeds this voltage for NbTi circuits.

  Therefore, as shown in FIG. 3, a larger voltage can be handled by connecting IGBTs in series. FIG. 3 shows a configuration method of the high withstand voltage protection resistance short-circuit switch.

  IGBTs (9a, 9b, 9c, 9d) are connected in series, snubbers (10a, 10b, 10c, 10d) are attached to each IGBT, and when the IGBT is off, the voltage generated in the circuit is applied to each IGBT. Dividing resistors (11a, 11b, 11c, 11d) were installed so that the voltages were equally shared.

  The voltage dividing resistance is set to less than 10% of the IGBT off-resistance so as not to be affected by the IGBT off-resistance. In this example, an element in a two-element one-package with a maximum collector-emitter voltage of 1700 V and a continuous collector current of 800 A was used, and the switch on the Nb3Sn coil side had a two-stage IGBT configuration and the NbTi side had a four-stage configuration.

Strictly speaking, when switching the IGBTs in series from the on-state to the off-state, the current-limiting operation of the IGBTs is not equal, and therefore there is a possibility that a difference in voltage sharing among the individual IGBTs occurs. However, due to the presence of the voltage dividing resistor and the snubber, variation in the shared voltage is suppressed, and the voltage applied to the IGBT can be suppressed within an allowable range.
(Main circuit disconnection switch and power cutoff switch)
Next, the main circuit dividing switch and the power cutoff switch will be described. Unlike the protective resistance short-circuit switch, the main circuit switch and the power cut-off switch are characterized in that a current always flows in a steady state. Therefore, these switches are required to have a sufficiently small on-resistance and a small voltage drop. When semiconductor elements are used, IGBTs are disadvantageous because the collector-emitter saturation voltage remains at 2-3V, and using MOSFETs can achieve on-resistance well below 1mΩ in parallel connection, but the withstand voltage is low. It is difficult to use. Therefore, an electromagnetic contactor is the most suitable switch to be put in the main circuit.

  FIG. 4 shows an example of the configuration of the main circuit disconnecting switch or the power cutoff switch. It consists of a magnetic contactor (12) and a snubber (10). Since these switches cut off the direct current when the contacts are opened and closed, an arc is generated between the contacts at the time of breaking, so that a snubber for suppressing high voltage is required.

  FIG. 5 shows another example of the configuration of the main circuit disconnecting switch or the power cutoff switch. There is a possibility that the sum of the half of the maximum generated voltage on the Nb3Sn circuit side and the half of the maximum generated voltage on the NbTi circuit side may be applied to the main circuit dividing switch (3) in FIG. A large circuit breaker (for example, a vacuum circuit breaker) having a sufficient withstand voltage against the applied voltage may be used. However, since using a large vacuum circuit breaker is costly and costly, as shown in Fig. 5, multi-stage connection of magnetic contactors (12a, 12b, 12c, 12d) is required, as is the case with a protective resistance short-circuit switch. It is desirable to use a voltage dividing resistor (11a, 11b, 11c, 11d) to share the voltage when the switch is turned off.

  This multi-stage connection eliminates the problem of voltage sharing when the switch is off, but it is necessary to cut off the large DC current, so if the switch is configured with only an electromagnetic contactor, the current is cut off. It is possible that contact burnout due to high voltage generation at the moment of operation and switch-off is insufficient.

  In that case, it is necessary to reduce or reduce the current to zero so that the electromagnetic contactor can be reliably turned off. For this purpose, a semiconductor switch is inserted into a switch that cuts off the main circuit current, and the current of the main circuit is commutated to the protection circuit using this switch. Since a magnetic commutator cannot control the current commutation speed, a large voltage is generated during the off operation. However, in the case of a semiconductor switch, the current commutation speed can be limited by controlling the gate control voltage. Generation of high voltage during commutation can be suppressed.

FIG. 6 shows a configuration example of a main circuit separation switch (a power cut-off switch may have this function) in which a semiconductor switch is inserted to control the commutation speed. In this configuration, a two-stage electromagnetic contactor (12a, 12b) and a MOSFET (13) are connected in series to form a switch. In addition, snubbers (10a, 10b, 10c) are installed in each switch, but this configuration is a design matter and may be determined appropriately. Sharing resistors (11a, 11b, 11c) are required to share the voltage applied when the switch is off, but MOSFET (13) has a small voltage that can be applied, typically several tens of volts, so MOSFET (13) In order to reduce the voltage applied to the resistor, the value of the sharing resistor (11b) needs to be set appropriately smaller than the other sharing resistors (11a, 11c). In addition, if the gate voltage of the MOSFET (13) is controlled so that the current is commutated sufficiently slowly and the electromagnetic contactors (12a, 12b) are opened at zero current, the operation shown in FIG. Can be snubbered. FIG. 7 is a circuit diagram showing an example of the configuration of a snubberless main circuit disconnecting switch or a power shutoff switch that enables control of the current commutation time.
(Protection circuit details)
Next, FIG. 8 shows an example of the configuration of the entire circuit of this embodiment. Four Nb3Sn coils (1a, 1b, 1c, 1d) form one coil block, and six NbTi coils (1e, 1f, 1g, 1h, 1i, 1j) form another coil block for two protections We decided to protect the magnet with a circuit.

  The Nb3Sn coil has two 1.7Ω protection resistors (7a, 7b), and the circuit protects the coil with a 3.4Ω protection resistor. The protection resistors (7a, 7b) have two IGBTs (9a, 7b). Shorted at 9b) and grounded via a 10kΩ grounding resistor (16a) at the midpoint of the protective resistor. A diode (14a, 14b) was inserted between the protection circuit and the coil block to suppress the current shunting during excitation. In the Nb3Sn coil protection circuit, a maximum voltage of about 2.4 kV is generated, and the ground voltage is 1.2 kV due to the midpoint installation. The IGBT (9a, 9b) with a collector-emitter voltage of 1700V and a continuous collector current of 800A was used.

  The NbTi coil side has 1.8Ω protection resistors (7c, 7d, 7e, 7f) in four stages, and the circuit protects the coils with 7.2Ω protection resistors, and the protection resistors (7c, 7d, 7e, 7f) Was short-circuited by four-stage IGBT (9c, 9d, 9e, 9f) and grounded via a 10kΩ grounding resistor (16b) at the midpoint of the protective resistance. A diode (14c, 14d) was inserted between the protection circuit and the coil block to suppress the current shunting during excitation. The NbTi coil protection circuit generates a maximum voltage of about 5kV, and the ground voltage is 2.5kV due to the midpoint installation. IGBTs (9c, 9d, 9e, 9f) with a collector-emitter voltage of 1700 V and a continuous collector current of 800 A were used.

  The main circuit disconnect switch was composed of magnetic contactors (12b, 12c). For the power cut-off switch, an electromagnetic contactor (12a) and MOSFET (13) connected in series are inserted between the DC current source (4) and the Nb3Sn coil block, and the electromagnetic switch is connected between the power supply and the NbTi coil block. A contactor (12d, 12e) connected in series was inserted. As the magnetic contactors (12a, 12b, 12c, 12d, 12e), those having an insulation withstand voltage of 2 kV and a rated current capacity of 800 A were used. The MOSFET (13) was configured by arranging 12 elements in parallel (not shown) having a maximum drain-source voltage of 150 V, a continuous drain current of 375 A, and a nominal on-resistance (maximum of 11 mΩ). The voltage dividing resistors (11g, 11i, 11j, 11k, 11m) attached to the magnetic contactor were 1 MΩ, respectively, and the voltage dividing resistor (11h) attached to the MOSFET (13) was 100 kΩ. The diodes (15a, 15b) were grounded so as to bypass the direct current source (4). Although the snubber is not shown in the drawing, the snubber is designed so as to recover the energy stored in the inductance corresponding to the change in the current path during the switch operation as seen from the individual switches.

  In the present embodiment, the voltage dividing resistor as described in the basic circuit is not installed in the protective resistor short-circuit switch, and is shared with the protective resistor. As shown in FIG. 9 (another example of the configuration of the entire circuit), a voltage dividing resistor may be installed, and the protection resistor middle point and the protection resistor short-circuit switch may not be connected. In this case, the ground resistance can be omitted.

  FIG. 10 is a circuit diagram showing another basic concept of the magnet protection circuit of the present invention. In the embodiment, the protection resistance short-circuit switch is connected to both ends of the protection resistance so that the protection resistance of each coil block is not visible, but it is also possible to short-circuit only a part of the protection resistance as shown in FIG. This is utilized when the temperature rise of the magnet is severe since the energy of the magnet can be recovered by the protection resistance that is not short-circuited until each protection resistance short-circuit switch is turned off.

10 is different from the circuit diagram of FIG. 1 in that protective resistors (7a ', 7b') are connected in series to protective resistors (7a, 7b), and protective resistors (7c ', 7d) are connected to protective resistors (7c, 7d). ') Connected in series, protective resistor short-circuit switch (8a) connected in parallel with protective resistor (7a, 7b), protective resistor short-circuit switch (8b) connected in parallel with protective resistor (7c, 7d) It is.
(Switch drive circuit)
As described above, the operation timing of each switch is determined by turning on the protective resistance short-circuit switch immediately before turning off the main circuit disconnection switch and power shutoff switch that cuts off the main circuit current, and the main circuit switch is turned off completely. After that, it is necessary to turn off the protective resistance short-circuit switch, and it is necessary to control the operation timing of the switch.

  In order to ensure the reliability of the protection operation, a mechanism for ensuring the time difference of the switch operation and operating without a controller for controlling the timing is required. FIG. 911 shows an example of a switch drive circuit for ensuring a time difference in switch operation without timing control. The drive circuit has a structure in which a plurality of isolated DC / DC converters are suspended from one main power source, and a capacitor and resistor delay circuit are connected to the output of each DC / DC converter. Each output is connected to the IGBT gate of the protective resistance short-circuit switch and the MOSFET gate constituting the main circuit switch. All IGBTs and MOSFETs should be normally open. The contactor should be configured normally open so that it turns off when the power supply stops. However, since the capacity of the capacitor is limited, it is impossible to secure a time difference by supplying power from here. . Therefore, a power source for driving the magnetic contactor (a constantly supplying system and a backup battery configuration) is connected via a MOSFET switch, and a control output is connected to the MOSFET switch. By appropriately setting the discharge time constant of the capacitor in the delay circuit, each switch can be operated with an appropriate time difference without a timing controller.

As described above, it is possible to safely separate individual protection circuits when a quench occurs, and thus it is possible to provide a system capable of protecting a superconducting magnet during a quench without limiting the size of the magnet and stored energy.
(Use of the magnet protection circuit of the present invention)
The magnet protection circuit of the present invention can be applied not to the permanent current mode operation but to a superconducting magnet to which current is supplied from a power source. It is particularly useful for magnets with large stored energy, and is optimal for applications such as superconducting magnets for fusion and SMES.

  The magnet protection circuit of the present invention can be applied not to the permanent current mode operation but to a superconducting magnet to which current is supplied from a power source. It can be used for applications such as fusion superconducting magnets and SMES superconducting magnets with large stored energy.

1a, 1b, 1c, 1d, 1e, 1f, 1g, 1h, 1i, 1j: Coil
2a, 2b: Coil block
3: Main circuit disconnect switch
4: DC current source
5a, 5b: Power cutoff switch
6: Power supply protection resistance or power supply internal resistance
7a, 7b, 7c, 7d, 7e, 7f: Protection resistance
7a ', 7b', 7c ', 7d': Protection resistance
8a, 8b: Protection resistance short-circuit switch
9,9a, 9b, 9c, 9d, 9e, 9f: IGBT
10,10a, 10b, 10c, 10d: Snubber
11a, 11b, 11c, 11d, 11e, 11f, 11g, 11h, 11i, 11j, 11k, 11m: Voltage divider resistor
12,12a, 12b, 12c, 12d, 12e: Magnetic contactor
13: MOSFET
14a, 14b, 14c, 14d: Diode
15a, 15b: Diode
16a, 16b: Ground resistance

Claims (11)

In a superconducting magnet configured by connecting a plurality of coil blocks and a power supply in series,
A first switch provided between the plurality of coil blocks;
A second switch provided between the coil block and the power source;
A protective resistance circuit connected in parallel with the coil block;
A third switch connected to the protective resistance circuit,
The coil block is configured by one coil or a plurality of coils connected in series,
The third switch is configured such that the resistance value of the protective resistance circuit is changed by switching the open / close state,
In the normal operation of the superconducting magnet, the first switch and the second switch are operated in a closed state, and the third switch is operated in an open state or a closed state.
When the superconducting magnet transitions to the normal conduction state, the third switch is closed, the first switch and the second switch are opened, and then the third switch is opened. A superconducting magnet characterized by being in a state. The superconducting magnet according to claim 1,
The first switch, the second switch, or the third switch is configured by connecting a plurality of switches in series. The superconducting magnet according to claim 1 or 2,
A resistance voltage divider for distributing a voltage applied to a switch is configured by being connected in parallel with the first switch, the second switch, or the third switch. magnet. The superconducting magnet according to any one of claims 1 to 3,
A superconducting magnet, wherein the first switch, the second switch, or the third switch includes a semiconductor switch element. The superconducting magnet according to any one of claims 1 to 4,
The first switch or the second switch includes a magnetic contactor that cuts off a current by opening and closing a contact, and a semiconductor switch that controls the magnitude of the current. The superconducting magnet according to claim 5,
The plurality of coil blocks, the power source, the first switch, and the second switch form a main circuit,
The first switch or the second switch is configured to transfer the current flowing in the main circuit to the protection resistor circuit by the semiconductor switch and reduce the current flowing in the main circuit, and then by the electromagnetic contactor. A superconducting magnet that cuts off current. The superconducting magnet according to any one of claims 1 to 6,
A superconducting magnet, which is grounded at the midpoint of each protective resistor connected to the coil block. The superconducting magnet according to any one of claims 1 to 6,
A superconducting magnet, wherein a ground point is grounded from a midpoint of each protective resistor connected to the coil block. The superconducting magnet according to any one of claims 1 to 6,
A superconducting magnet, wherein a ground point is grounded from a middle point of each protective resistor connected to the coil block via a fourth switch. The superconducting magnet according to claim 9,
In the normal operation of the superconducting magnet, the fourth switch is opened,
In the normal conduction transition of the superconducting magnet, after the first switch and the second switch are opened, and before the third switch is opened, the first switch 4. A superconducting magnet, wherein the switch 4 is closed. The superconducting magnet according to any one of claims 1 to 10,
The third switch is a superconducting magnet, wherein the resistance value of the protective resistance circuit is changed by short-circuiting all or a part of the protective resistance circuit.